We propose to evaluate virus-load in lymph nodes and other tissues involved in the HIV-pathogenesis in vivo. Although quantitative cell cultures and plasma viremia are extremely useful indicators of the circulating virus in the blood, these assays do not assess the virus-burden locally in the affected tissues. Further, because of the increasing frequency of HIV-related lymphomas and the recognized significance of neurologic complications in these individuals, it is important to identify target cells and focal areas of HIV infection in various tissues. Our project therefore will focus on the quantitative assessment of HIV-infected cells by in situ molecular hybridization of mRNA, RNA/DNA PCR as a confirmatory test and immunohistochemical staining for the identification of cell types in situ. The proposal is also based on the fact that our ATEU has one of the largest patient population of AIDS-related lymphoma in the country and a significant number of specimens are already available from the ACTG-studies that have been completed or closed to accrual. This offers a unique opportunity to study sequential samples from clinically well-defined patients with distinct pathologic manifestations and to develop a useful clinical test on specimens that are routinely obtained for diagnosis and treatment of these patients.